During elevator modernization projects in occupied buildings after the first elevator car is modernized, it will be put into service while other cars are modernized. A new or newly-installed elevator car controller will perform dispatching for the new car, while the yet-to-be-modernized, older or previously-installed cars will still be controlled by the old or previously-installed control system, including dispatching. As each old elevator car becomes modernized, it switches its control from the old to the new system. During this process of adding cars to the new controller and deleting cars from the old control system, two separate dispatching control systems are operating independently in the same building. For example, it may be the case that there are more than one set of up and down hall call push-buttons at each floor landing. In that case, after modernization of the first car, the new control system may be hooked up to one set of push-buttons at each floor, while the other push-buttons at the same floor remain hooked up to the old control system. In the event that a prospective passenger at a landing elects to select his up or down destination by pushing an up or down push-button associated with the old control system, only the old elevator cars will respond to his call. On the other hand, if another prospective passenger arrives at the same landing at the same time and pushes a similar destination direction on the new car's push-button, both the old and new systems will be attempting to respond to a demand at the same floor in the same direction and both may arrive at about the same time, thereby causing dispatching inefficiencies.
It would be desirable to solve this and other similar problems of dispatching inefficiency during the modernization process and at other times.